In the fabrication of semiconductor devices, marks of numerical or alphanumerical numbers are frequently placed on surfaces of semiconductor substrates for identification purpose. The identification marks are provided such that different lots of semiconductor substrates can be tracked in the numerous fabrication processes. For instance, the identification marks can be used for identifying a defectively manufactured batch of substrates when a quality problem or defect has been discovered. The identification marks may also be used to conveniently identify different lots of semiconductor substrates that have different characteristics or properties.
Traditionally, identification marks on semiconductor substrates, such as silicon wafers, are provided by using a laser scribing technique wherein an identification mark is directly scribed into a top surface layer of a silicon wafer. During such scribing process, dots or spots are generated in the surface of a silicon wafer by melting the silicon material with a high-intensity energy beam such as laser. The high-intensity, focused laser beam is absorbed very close to the wafer surface. The: degree of absorption is dependent upon the wavelength of the laser used, the type of the laser used, the pulse length and many other factors. When laser is used to make a mark in silicon, the laser beam pause heats up the material until it melts. A crater is thus formed which has a circular ridge around a dot or bulge in a melted zone.
Contamination problems are frequently caused by a laser scribing process conducted in a silicon surface. For instance, debris can be generated when the liquified silicon material is ejected as droplets and then propelled by the expansion of the vapor formed. The liquid droplets fall to the surface of the wafer and then solidify into splatter debris. In a later processing step, when the wafer surface is pressed down by a wafer holding device such as a clamp ring, the splattered debris shatters and separates from the wafer surface becoming contaminating particles.
In a semiconductor fabrication process based on silicon wafers, an ideal time to mark the wafer for achieving a debris-free marking is to perform the task on a bare silicon surface, prior to the deposition of any other material layers on top. In practice, however, present fabrication process prefers to mark the wafer with a lot number after one or more wafer processing steps have been performed on the bare silicon. For instance, after a gate oxide layer or a silicon nitride insulating layer has been deposited on top of the bare silicon. A delayed marking, process on a silicon wafer enables a more flexible fabrication process to be carried out on a production line by keeping work-in-progress wafer inventory down. Another reason for delaying the marking of wafers is that once the wafer is marked, it is dedicated to a specific chip design or to a customer.
An undesirable side effect of delaying the wafer marking process is that it becomes more difficult to obtain a splatter-free or a debris-free mark on the wafer, since the various deposited layers on the silicon surface have different laser absorption characteristics and thus, melt or disintegrate differently under a high-intensity laser beam. Furthermore, due to the thickness of the additional material layers on top of the silicon surface, more splattered material is generated which presents opportunities of producing more contaminating particles when such splattered material is later crushed by a wafer holding device.
It is therefore an object of the present invention to provide a splatter-free, debris-free wafer marking method that does not have the drawbacks or shortcomings of the conventional wafer marking methods.
It is another object of the present invention to provide a debris-free marking method for electronic substrates wherein a high-intensity energy beam is not used to scribe directly into a substrate surface.
It is a further object of the present invention to provide a debris-free marking method for electronic substrates by utilizing a tape of polymeric material and marking the tape with an identification mark by a high-intensity energy beam.
It is another further object of the present invention to provide a debris-free marking method for a silicon wafer by first marking a polymeric tape with an identification mark and then adhering the tape to the wafer surface and carrying out an etching process.
It is still another object of the present invention to provide a debris-free marking method for a silicon wafer by first marking a polymeric tape within an identification mark and then adhering the tape to the wafer surface for exposing to a dry etchant in a reactive ion etching process.
It is yet another object of the present invention to provide a debris-free marking method for a silicon wafer by first marking a polymeric tape within an identification mark and then laminating the tape to a wafer surface and exposing the wafer to a wet etchant in a wet dipping process.
It is still another further object of the present invention to provide a debris-free marking method for a silicon wafer by first marking a polymeric based tape, adhering the tape to the silicon wafer and then exposing the wafer to a first etchant effective in etching through a first insulating layer, and then exposing the wafer to a second etchant effective in etching through a second insulating layer for reproducing the identification mark.
It is yet another further object of the present invention to provide a debris-free marking method for a thin film transistor substrate by first marking a polymeric tape with an identification mark, gluing the tape to the substrate and then reproducing the mark in the substrate surface by an etching process.